how to deactivate Download Monitor button from posts visual editor?

I’m not sure we add a button to the visual editor, other than the ‘Insert Download’ button above the editor. What ‘visual editor’ button are you talking about?

yes i mean the ‘Insert Download’ button above the editor. i want to remove it for all users only authors or remove it totally for all users.

This isn’t possible by default. You can try to remove the filters/actions that add the button but this would be considered custom development and unfortunately I can’t help you with this.

where can i find this filter/actions in your plugin files?

What you’re looking for here is custom development and unfortunately I can’t help you with that. I suggest you ask your question somewhere created for these kind of questions like wordpress.stackexchange.com or consider hiring a developer.